Past fuel filter assembly designs have provided the user with a rough but usable estimate of the condition of the filter element as a function of the height of the fuel level in an upper filter chamber of the fuel filter assembly during operation of the engine. In these designs, fuel moves from a lower chamber of the fuel filter assembly, through a passage, to the upper chamber of the fuel filter assembly. The fuel passes through a cylindrical filter element and out to the engine through an opening at the lower center of the upper chamber. An opaque or transparent cover of the upper filter chamber allows the user to view the fuel level within the upper chamber of the fuel filter assembly so that the user may use the fluid level within the upper chamber as a rough estimate as to the condition of the filter element.
Generally speaking, the fuel level tends to rise in the upper chamber as the filter element becomes more and more clogged from the bottom of the filter element to the top of the filter element. When the fuel level reaches the top of the filter element in normal operation, this may be taken as the time to consider changing the filter element.
Such fuel filter systems generally run by vacuum, that is, a fuel pump is positioned downstream of the fuel filter assembly, such that the pump is pulling or drawing fuel through the fuel filter assembly. When the fuel pump is placed upstream from the fuel filter assembly, the system is pressurized, and the fuel level within the upper chamber of the fuel filter assembly does not respond in the same manner as the system under vacuum. During low pressure applications, the fuel level may respond in a manner whereby the fuel level can be used to estimate the condition of the filter element. However, under high pressure applications, the fuel level within the upper chamber of the fuel filter assembly rises to the top of the upper chamber immediately, and therefore, does not provide the benefit of having the fuel level provide an estimate as to the condition of the filter element. The inability to run such fuel filter assemblies under high pressure applications reduces the flexibility and applications by which such fuel filter assemblies may be utilized.
It would be desirable to provide a fuel filter assembly that could be used under high pressure applications while still providing the benefits of having the fuel level in the upper chamber of the fuel filter assembly provide an indicator as to the general condition of the filter element.